Contact-sensitive pressure-sensitive conductive composite electrode and method for ablation

ABSTRACT

A catheter assembly for pressure-sensitive control of ablation treatment is disclosed. The assembly includes a conductive element, an electrode, and a pressure sensitive conductive composite member positioned between the conductive element and the electrode. At least one of the conductive pin, the pressure sensitive conductive composite element and the ablation electrode are moveable to create an engagement position and a non-engagement position. In the engagement position, the elements are electrically coupled such that ablation energy may be delivered from the conductive pin to the ablation electrode via the pressure sensitive conductive composite element. In the non-engagement position, the elements are electrically decoupled such that ablation energy is not delivered to the ablation electrode. A related method for pressure-sensitive control of ablation is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. application Ser. Nos. 11/647,316filed 29 Dec. 2006 (Attorney Docket No. OB-050800US/82410.0084; entitled“Pressure-Sensitive Conductive Composite Electrode and Method forAblation”); 11/647,314 filed 29 Dec. 2006 (Attorney Docket No.OB-047700US/82410.0006; entitled “Pressure-Sensitive ConductiveComposite Contact Sensor and Method for Contact Sensing”); 11/647,279filed 29 Dec. 2006 (Attorney Docket No. OB-047701 US/82410.0164;entitled “Design of Ablation Electrode with Tactile Sensor”) all ofwhich are hereby incorporated by reference as though fully set forthherein.

BACKGROUND OF THE INVENTION

a. Field of the Invention

The present invention pertains generally to an electrophysiologicaldevice and method for providing energy to biological tissue and, moreparticularly, to an ablation apparatus with greater contact sensitivity.

b. Background Art

Ablation devices, including radio frequency (“RF”) ablation devices,have heretofore been provided, but not using a pressure sensitiveconductive composite (“PSCC”) based electrodes (including, for example,quantum tunneling composites (“QTC”) and other pressure-sensitive,conductive polymers).

Many medical procedures, including for example, creating lesions withelectrical energy, rely on good contact between the medical device andthe tissue. In some catheter applications, the point of electrode-tissuecontact is typically 150 cm away from the point of application of force.This gives rise to functional and theoretical challenges associated withconventional devices, and thus, the ability to accurately assess tissuecontact is increasingly important, especially in connection withablation treatment.

There is a need for improved ablation devices that provide greatercontact sensitivity for control of ablation treatments using electricalenergy.

There is a need for improved ablation devices that provide greatercontact sensitivity for RF ablation treatments.

There is also a need for improved ablation devices that betterconcentrate the RF energy to the region of tissue that is in contactwith the electrode.

BRIEF SUMMARY OF THE INVENTION

Disclosed herein is an electrode assembly having a conductive pin forconducting ablation energy; an ablation electrode at a distal end of theelectrode assembly; and pressure sensitive conductive composite elementdisposed between the conductive pin and the ablation electrode. Thepressure sensitive conductive composite element is positioned such thatwhen it is compressed between the conductive pin and the ablationelectrode, the pressure sensitive conductive composite element conductsablation energy from the conductive pin to the ablation electrode. Theelectrode assembly may also contain a first shaft in which the ablationelectrode is disposed at a distal end; a second shaft in which theconductive pin is disposed; and a spring that permits the first andsecond shafts to be compressed toward each other. Optionally, collars oranchors may be established on each of the first and second shafts suchthat the spring may be anchored between the two collars duringcompression.

Also disclosed is a catheter assembly for conducting ablative energyhaving a catheter body with an ablation electrode; a pressure sensitiveconductive composite member; a conductive pin for conducting ablationenergy; and a spring that is capable of being in at least a first stateand a second state. The first state is one in which the springelectrically decouples the electrode from at least one of the conductivepin and the pressure sensitive conductive composite member. The springis also compressible into a second state wherein pressure is applied tothe pressure sensitive conductive composite member to place it in aconductive state, thereby transferring ablation energy from theconductive pin to the ablation electrode. Optionally, one or morepressure transfer members may be disposed between the pressure sensitiveconductive composite member and the ablation electrode. Ideally, thepressure transfer members are disposed such that pressure applied to theablation electrode is transferred through the at least one pressuretransfer member to the pressure sensitive conductive composite member.

Also disclosed is a method of treating tissue. An electrode assembly isprovided having a conductive element for conducting RF energy and anablation electrode at a distal end of the electrode assembly. A pressuresensitive conductive composite member is disposed between the conductiveelement and the ablation electrode. The electrode assembly may bepositioned in contact with a tissue to be treated, and the operatorexerts sufficient force upon the tissue through the electrode assemblysuch that the pressure sensitive conductive composite member becomesconductive and permits the delivery of RF energy to the tissue.Preferably, the ablation assembly is configured such that at least twoof the conductive element, the ablation electrode and the pressuresensitive conductive composite element may be in an electricallydecoupled state, but after moving at least one of the conductiveelement, the ablation electrode and the pressure sensitive conductivecomposite element, the elements are electrically coupled such thatablation energy may be delivered from the conductive pin to the ablationelectrode via the pressure sensitive conductive composite element.Optionally, control signals may be used to control the RF generator thatprovides the RF ablation energy. For example, if the degree of contactis assessed such that it is determined that there is an insufficientdegree of contact, the RF generator may be disabled to precludeablation. Alternatively, the tissue/electrode interface may be monitoredfor commencement of the delivery of ablation energy, and then, a timermay be executed such that the RF generator is disabled after havinggenerated RF energy for a fixed time period.

An electrode assembly is also disclosed having a conductive pin forconducting ablation energy; an ablation electrode at a distal end of theelectrode assembly; a pressure sensitive conductive composite elementdisposed between the conductive pin and the ablation electrode; and anengagement assembly. The engagement assembly moves at least one of theconductive pin, the pressure sensitive conductive composite element andthe ablation electrode to create an engagement position and anon-engagement position. The engagement position electrically couplesthe conductive pin, the pressure sensitive conductive composite elementand the ablation electrode, such that ablation energy may be deliveredfrom the conductive pin to the ablation electrode via the pressuresensitive conductive composite element. The non-engagement positionelectrically decouples at least two of the conductive pin, the pressuresensitive conductive composite element, and the ablation electrode, suchthat ablation energy is not delivered to the ablation electrode. Theengagement assembly may comprise: a first shaft in which the ablationelectrode is disposed at a distal end; a second shaft in which theconductive pin is disposed; and a spring that permits the first andsecond shafts to be compressed toward each other.

Each of the embodiments of the present invention utilizes a pressuresensitive conductive composite medium. Of course, the pressure sensitiveconductive composite element may also comprise a quantum tunnelingcomposite material.

An objective of the present invention is to provide a PSCC electrodethat may be used for RF ablation treatment.

Another object of the present invention is to provide a method ofmanufacturing an electrode assembly for ablation therapy.

Another object of the present invention is to provide a flexible,pressure-sensitive, conductive polymer-based electrode for RF ablation,which can be used in a wide variety of tissue environments.

Yet another object of the invention is to provide an ablation electrodethat better concentrates the energy to the region of tissue that is incontact with the electrode.

Yet another object of the invention is to provide an ablation electrodethat mitigates edge-effects, hot spots and coagulum formation during theablation process.

A further object of the invention is to provide a system for RF ablationtreatment, including an RF generator and a coolant supply system thatcan be connected to a pressure-sensitive, conductive polymer-basedelectrode to provide control over the RF ablation process.

Another object of the present invention is to provide an electrode witha contact sensor assembly that can sense contact with tissue based onthe pressure that is exerted on the sensor, and then use the contactinformation for medical treatments (such as ablation).

Another object of the present invention is to provide an ablationelectrode with contact sensor that measures pressure that is beingexerted on the sensor based on direct or indirect contact between thesensor and another mass, such as tissue.

Yet another object of the present invention is to provide a method ofablation using contact sensing.

Still another object of the present invention is to provide ainexpensive, flexible, contact sensitive electrode for dry surfaceapplications.

Another object is to improve the efficiency, safety and efficacy of dryRF ablation devices.

Another object is to prevent arcing during dry RF ablation treatments.

Yet another object of the present invention is to provide a method ofmanufacturing an electrode having a pressure-sensitive, conductivepolymer-based contact sensor.

Yet another objective of this invention is to provide a method for RFablation that utilizes a pressure-sensitive, conductive polymer-basedelectrode in accordance with the teachings herein.

Another objective of the present invention is to provide a PSCC-basedsensor that may be used in connection with RF ablation treatment.

An advantage of using a PSCC in ablation applications is that the PSCCmitigates arcing.

Another advantage of using a PSCC in an ablation device is that thedesign may be significantly less complicated, which permits reducedmanufacturing costs and increased reliability.

The foregoing and other aspects, features, details, utilities, andadvantages of the present invention will be apparent from reading thefollowing description and claims, and from reviewing the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are perspective views of a sample embodiment of thepresent invention, illustrating how the present invention may be used toassess contact with tissue and ablate tissue.

FIG. 2 is a side view drawing of an exemplary catheter having a PSCCelectrode.

FIGS. 3A and 3B are cross sectional views that demonstrate the contactpressure at the electrode-tissue interface.

FIGS. 4A and 4B are cross-sectional views of a preferred embodiment of acatheter having a PSCC electrode.

FIGS. 5A and 5B are cross-sectional views of another preferredembodiment in which the PSCC electrode is in the shape of a helix.

FIGS. 6A and 6B are cross-sectional views of another preferredembodiment in which the PSCC electrode is located about an innerconductive core.

FIGS. 7A and 7B are cross-sectional views of another preferredembodiment in which the PSCC electrode is in the shape of a mesh.

FIGS. 8A and 8B are cross-sectional views of another preferredembodiment in which the PSCC electrode is formed as an outer substratelayer.

FIGS. 9A and 9B are cross-sectional views of yet another preferredembodiment of the invention with thermal sensing.

FIGS. 10A and 10B are cross-sectional views of another preferredembodiment in which the PSCC electrode is adjacent a heat sink.

FIG. 11 is a side view of another preferred embodiment of the inventionin which the catheter includes a coolant efflux hole.

FIGS. 12A and 12B are cross-sectional views of the embodiment of FIG. 6,in which efflux hole 186 has been added.

FIGS. 13A and 13B are cross-sectional views of a modified version of theembodiment of FIG. 12A with thermal sensing.

FIG. 14 is a side view of an embodiment that is a modified version ofthe embodiment of FIG. 11 with a heat sink.

FIGS. 15A and 15B are cross-sectional views of a modification of theembodiment of FIG. 12 with a heat sink.

FIGS. 16A and 16B are cross-sectional views of yet another embodiment ofthe present invention.

FIGS. 17A, 17B and 17C are side views of another preferred embodimentthat utilizes a spring to create a contact sensitive RF ablationassembly.

DETAILED DESCRIPTION OF THE INVENTION

A contact-sensitive PSCC electrode for ablation is disclosed, along withmethods for using and methods of manufacturing the PSCC-based electrode.

When used in this application, the terms “pressure sensitive conductivecomposite” and “PSCC” mean a pressure sensitive conductive compositethat has unique electrical properties as follows: the electricalresistance of the PSCC varies inversely in proportion to the pressurethat is applied to the PSCC. The PSCC material that is most useful withthe present invention has a high electrical resistance when not understress (that is, in a quiescent state), and yet the same PSCC materialstarts to become conductive under pressure, and indeed, the electricalresistance may fall to less than one ohm (1 Ω) when under sufficientpressure. When in a quiescent state, the PSCC material preferably has aresistance that is greater than 100,000 ohms, and more preferably,greater 1M ohms, and most preferably, the PSCC material is anon-conductor in its quiescent state (e.g., having a resistance greaterthan 10M ohms). Preferably, the PSCC material will also meet cytotoxity,hemolysis, systemic toxicity and intracutaneous injection standards.

The present invention will work with various pressure sensitiveconductive composite materials. For example, U.S. Pat. No. 6,999,821(which is incorporated by reference herein as if fully set forth below)discloses a conductor-filled polymer that may be useful in the presentinvention. As disclosed therein, conductor-filled polymers may includepresently available materials approved for implantation in a human bodysuch as silicone rubber with embedded metallic, carbon or graphiteparticles or powder. Silver filled silicone rubbers of the kindmanufactured by NuSil or Specialty Silicone Products, modified so as tobe approved for implantation, are of potential utility. An example issilver-coated, nickel-filled silicone rubber sold as NuSil R2637. Thesubstrate need not be silicone; for example, it is contemplated thatother insulating or weakly conductive materials (e.g., non-conductiveelastomers) may be embedded with conductive materials, conductive alloysand/or reduced metal oxides (e.g., using one or more of gold, silver,platinum, iridium, titanium, tantalum, zirconium, vanadium, niobium,hafnium, aluminum, silicone, tin, chromium, molybdenum, tungsten, lead,manganese, beryllium, iron, cobalt, nickel, palladium, osmium, rhenium,technetium, rhodium, ruthenium, cadmium, copper, zinc, germanium,arsenic, antimony, bismuth, boron, scandium and metals of the lanthanideand actinide series and if appropriate, at least one electroconductiveagent). The conductive material may be in the form of powder, grains,fibers or other shaped forms. The oxides can be mixtures comprisingsintered powders of an oxycompound. The alloy may be conventional or forexample titanium boride.

Other examples of an acceptable PSCCs for use in the present inventioninclude quantum tunneling composites (“QTC”), such as those availablethrough Peratech Ltd. (of Darlington, UK), including the QTC pill, theQTC substrate and the QTC cables. The QTC materials designed by PeratechLtd. have variable resistance values that range from >10M ohms (in theabsence of stress) to <1 ohm when under pressure. Ideally, the QTC wouldmeet cytotoxity, hemolysis, systemic toxicity and intracutaneousinjection standards.

Other examples of PSCC materials that may be used in the presentinvention include the conductive polymers described and disclosed inU.S. Pat. Nos. 6,646,540 (“Conductive Structures”); 6,495,069 (“PolymerComposition”); and 6,291,568 (“Polymer Composition”); all of theforegoing patents are incorporated by reference as if set forth below intheir entireties. These materials as described has having a variableresistance of >10¹² Ohms before any stress is applied to less than 1 ohmwhen finger pressure is applied.

As a result of this unique property, PSCC materials may be described ashaving an ability to transform from an effective insulator to ametal-like conductor when deformed by compression, twisting, orstretching. The electrical response of a PSCC can be tuned appropriatelyto the spectrum of pressures being applied. Its resistance range oftenvaries from greater than 10 MΩ to less than 1Ω. The transition frominsulator to conductor often follows a smooth and repeatable curve, withthe resistance dropping monotonically to the pressure applied. Moreover,the effect is reversible in the sense that once the pressure is removed,the electrical resistance is also restored. Thus, a PSCC may betransformed from an insulator to a conductor, and back to an insulator,simply by applying the appropriate pressure. PSCCs have been known tocarry large currents (up to 10 Amps) and support large voltages (40 Vand higher).

Preferably, the PSCC being used in connection with the present inventioncan transform from an insulator (that is, conducting little or nocurrent) to an effective conductor simply by applying a small change inpressure to the PSCC. For example, by applying pressure with a hand, ormore particularly, with a finger, a surgeon can transform the PSCC froman insulator to a conductor to permit contact sensing.

The PSCC used in the present invention may also be chosen or customizedto be of a specific pressure sensitivity such that the transformationfrom an insulator to a conductor occurs over a wide or narrow range ofpressure. For example, highly sensitive PSCCs, which register a sharpchange in resistance with a finite amount of applied pressure, may bepreferred for soft contact applications such as the atrial wall. Lesssensitive PSCCs, which require more pressure to register the same amountof change in resistance, may be preferred for hard contact applicationssuch as ablation in ventricular walls.

Because a PSCC's resistance drops monotonically as pressure increases, aPSCC electrode is able to deliver energy for ablation gradually, andthen increasingly as pressure increases. Thus, the present inventionpermits ablation with a “soft start” and self-regulation of ablationcurrent based on contact pressure.

The present invention permits the creation of an electrode fabricated ofa PSCC that can differentiate between a soft and a hard push. Such adevice can be used to switch, for example, an ablation electrode inresponse to a concentrated pressure while ignoring the generalbackground pressure. Alternatively, such a device can “turn on” anddeliver electrical energy that is already present within the device.Thus, by utilizing electrodes made with PSCCs, the present inventionpermits an electrode for delivering electrical energy for ablation, andindeed, may be designed for self actuation to deliver the electricalenergy once the applied pressure exceeds a certain threshold.

Because a PSCC electrode may be used to deliver ablation with a “softstart,” the PSCC electrode of the present invention may be used indirect contact with the target tissue, thereby eliminating the physicalgap that sometimes exists with other ablation electrodes. Eliminatingthe gap reduces the possibility of arcing, and thereby improves thesafety and efficacy of ablation.

The unique properties of a PSCC permit the creation of novel andpressure-sensitive current-control devices for the direct control ofelectrodes for various forms of electrical energy, including RF energy.The unique properties permit the creation of novel andpressure-sensitive sensors to assess contact between the sensors andtissue that may be the subject of ablation.

FIGS. 1A and 1B illustrate a sample embodiment of the present invention.As illustrated in FIGS. 1A and 1B, PSCC electrode 105 includes acatheter shaft 90 and a contact surface 100 that extends from cathetershaft 90. In this embodiment, PSCC electrode 105 is flexible such thatwhen it comes into contact with tissue 12, PSCC electrode 105 isdeflected in direction 18 as illustrated in FIG. 1 b, and the deflectionpermits the activation of PSCC electrode 105 based on a degree ofcontact between PSCC electrode 105 and tissue 12.

FIG. 2 is a close-up of the sample embodiment depicted in FIGS. 1A and1B. FIG. 2 illustrates cross-sectional reference lines A-A and B-B,which will be used to illustrate preferred embodiment of the presentinvention.

As illustrated in FIG. 3A, when the PSCC electrode is in a relativelycontact free environment (such as air, or in the flowing blood streamwhile inside a blood vessel or heart chamber), the PSCC is an insulator.When used for an ablation application, however, the PSCC electrode isplaced against tissue as illustrated in FIG. 3B. As the contact pressureincreases, the PSCC becomes conductive and permits the degree of contactto activate and/or control operation of PSCC electrode. Because of theunique properties of a PSCC, only that portion of the PSCC electrodethat is in contact with the tissue becomes conductive. Those portionswhich are not in direct contact with the tissue, such as the regionfacing the blood, remain non-conductive, thereby mitigating any currentleakage that may cause coagulum and thrombus formation.

The resistance of a PSCC electrode changes anisotropically, based on thevariation of the contact pressure on the PSCC electrode. Thus, asillustrated in FIG. 3B, the contact pressure at the electrode-tissueinterface is maximum at the point (or line) of normal incidence andgradually decreases along the arc of contact to zero at the edge of thecontact. Because of its ability to direct RF energy to the point ofcontact, the electrode is omni-directional in use, buttissue-directional in application. The RF energy passes mostly into thetissue and minimally into the blood. This offers significant advantages,including increased efficiency, over other ablation electrodes.

FIGS. 4A and 4B illustrate a preferred embodiment of the presentinvention, revealing two cross sectional drawings taken along thereference lines of A-A and B-B as labeled in FIG. 2. In this preferredembodiment, the PSCC electrode 110 comprises: catheter shaft 90 and acontact surface 100 that extends from catheter shaft 90. Catheter shaft90 may be either conductive or non-conductive, and preferably, cathetershaft 90 is non-conductive. In this embodiment, the PSCC forms theworking surface of the electrode that is used for ablation therapy. Asdepicted in FIGS. 4A and 4B, PSCC electrode 110 comprises: flexibleinner conductive core 111; and an outer PSCC substrate layer 112, whichis mechanically and electrically coupled to the flexible innerconductive core 111. Flexible inner conductive core 111 may include aflat top (like the top of a right cylinder), or optionally it mayinclude a portion of a sphere on its distal end as illustrated in FIG.4A. Flexible inner conductive core 111 may be connected to an electricalconductor 114, which may be connected to an RF generator (e.g., RFcurrent source 80). In use, this preferred embodiment is used to ablatetissue (not shown) to which a reference electrode (not shown) has beenattached. PSCC electrode 110 ablates tissue by delivering ablationenergy through inner conductive core 111. Preferably, the referenceelectrode is grounded to an electrical ground.

As an alternative to the flexible embodiment discussed in the precedingparagraph, it is contemplated that the same structural design may beused to produce a less flexible (or even rigid) ablation device. Forexample, PSCC electrode 110 may comprise: a rigid inner conductive core111; and an outer PSCC substrate layer 112, which is electricallycoupled to the inner conductive core 111. Inner conductive core 111 maybe connected to an electrical conductor 114, which may be connected toan RF generator (e.g., RF current source 80). In use, this preferredembodiment is used to ablate tissue (not shown) to which a referenceelectrode (not shown) has been attached. PSCC electrode 110 ablatestissue by delivering ablation energy through inner conductive core 111.While the inner conductive core is rigid, the PSCC layer is deformablesuch that when the ablation electrode is pressed into the tissue, thePSCC becomes conductive and delivers RF energy to the tissue forablation purposes. In this embodiment, the PSCC may be coated with oneor more outer electrically-conductive layers (which may be rigid orflexible). In this further modification, the PSCC layer is sandwichedbetween at least two conductive coatings, and thus under pressure, theRF energy is delivered to the tissue via the rigid inner conductivecore, the compressible PSCC layer, and the one or more outerelectrically-conductive layers.

FIGS. 5A and 5B illustrate another preferred embodiment of the presentinvention, revealing two cross sectional drawings taken along thereference lines of A-A and B-B as labeled in FIG. 2. PSCC electrode 120extends from a catheter shaft 90, and PSCC electrode 120 comprises:flexible inner conductive coil 121 in the shape of a helix; and a PSCCsubstrate layer 122 within which the inner conductive coil 121 islocated. Flexible inner conductive coil 121 is connected to anelectrical conductor 114, which may be connected to an RF generator(e.g., RF current source 80). In use, this preferred embodiment is usedto ablate tissue (not shown) to which a reference electrode (not shown)has been attached. PSCC electrode 120 ablates tissue by deliveringablation energy through inner conductive coil 121. Preferably, thereference electrode is grounded to an electrical ground. PSCC electrode120, when pressure is asserted by tissue against contact surface 100,which reduces the internal impedance of the PSCC substrate.

FIGS. 6A and 6B illustrate yet another preferred embodiment of thepresent invention, revealing two cross sectional drawings taken alongthe reference lines of A-A and B-B as labeled in FIG. 2. PSCC electrode130 extends from a catheter shaft 90, and PSCC electrode 130 comprises:flexible inner conductive coil 131 in the shape of a helix; an outerPSCC substrate layer 132; and an electrically insulative flexible shaft133 located within the helix of the flexible inner conductive coil 131.Flexible shaft 133 may optionally include a portion of a sphere on itsdistal end as shown in FIG. 6A. Flexible inner conductive coil 131 isconnected to an electrical conductor 114, which may be connected to anRF generator (e.g., RF current source 80). In use, this preferredembodiment is used to ablate tissue (not shown) to which a referenceelectrode (not shown) has been attached. PSCC electrode 130 ablatestissue by delivering energy through inner conductive coil 131.Preferably, the reference electrode is grounded to an electrical groundreference signal. PSCC electrode 130, when pressure is asserted bytissue against contact surface 100, which reduces the internal impedanceof the PSCC substrate.

FIGS. 7A and 7B illustrate yet another preferred embodiment of thepresent invention, revealing two cross sectional drawings taken alongthe reference lines of A-A and B-B as labeled in FIG. 2. PSCC electrode140 extends from a catheter shaft 90, and PSCC electrode 140 comprises:flexible inner conductive sheath 141 formed of a mesh; an outer PSCCsubstrate layer 142; and an electrically insulative flexible shaft 143located interiorly of the flexible inner conductive sheath 141. Flexibleshaft 143 may optionally include a portion of a sphere at its distal endas shown in FIG. 7A. Flexible sheath 141 is connected to an electricalconductor 114, which may be connected to an RF generator (e.g., RFcurrent source 80). In use, this preferred embodiment is used to ablatetissue to which a reference electrode (not shown) has been attached.PSCC electrode 140 ablates tissue by delivering energy through theflexible sheath 141. Preferably, the reference electrode is grounded toan electrical ground reference signal.

FIGS. 8A and 8B illustrates yet another preferred embodiment of thepresent invention, revealing two cross sectional drawings taken alongthe reference lines of A-A and B-B as labeled in FIG. 2. PSCC electrode150 extends from a catheter shaft 90, and PSCC electrode 150 comprises:an electrically insulative flexible shaft 153; a flexible innerconductive layer 151 (formed, for example, as a coating and/or wraparound flexible shaft 153); and an outer PSCC substrate layer 152.Electrically insulative flexible shaft 153 and flexible inner conductivelayer 151 may optionally include a portion of a sphere at theirrespective distal ends (as illustrated in FIG. 8A). Flexible innerconductive core 151 is connected to an electrical conductor 114, whichmay be connected to an RF generator (e.g., RF current source 80). Inuse, this preferred embodiment is used to ablate tissue (not shown) towhich a reference electrode (not shown) has been attached. PSCCelectrode 150 ablates tissue by delivering ablation energy through theflexible inner conductive core 151. Preferably, the reference electrodeis grounded to an electrical ground reference signal.

FIGS. 9A and 9B illustrates yet another preferred embodiment of thepresent invention, revealing two cross sectional drawings taken alongthe reference lines of A-A and B-B as labeled in FIG. 2. PSCC electrode160 extends from a catheter shaft 90, and PSCC electrode 160 comprises:a thermally conductive, electrically insulative, flexible shaft 163; aflexible inner conductive layer 161 (formed, for example, as a coatingand/or wrap around flexible shaft 163, or as illustrated in FIG. 9, ahelix); an outer PSCC substrate layer 162; and a plurality of thermalsensors 164 located within the thermally conductive, electricallyinsulative, flexible shaft 163 to measure temperatures at variouslocations therein. Electrically insulative flexible shaft 163 andflexible inner conductive layer 161 may optionally include a portion ofa sphere at their respective distal ends (as illustrated in FIG. 9A).Flexible inner conductive coil 161 is connected to an electricalconductor 114, which may be connected to an RF generator (e.g., RFcurrent source 80). In use, this preferred embodiment is used to ablatetissue (not shown) to which a reference electrode (not shown) has beenattached. PSCC electrode 160 ablates tissue by delivering ablationenergy through the flexible inner conductive coil 161. Preferably, thereference electrode is grounded to an electrical ground referencesignal. As one of ordinary skill can appreciate, temperature sensors 164(such as thermistors, thermocouplers or other temperature sensors) canbe used to monitor operation temperature to help ensure effective andsafe ablation treatment. For example, one or more temperatures may beused at a variety of locations, include e.g., at a distal end at thedevice to monitor a temperature that is at least in part reflective ofthe tissue temperature, or even within the electrically insulativeshaft. Other potential locations include the use of a temperature sensorlocated at a location where the cooling fluid enters the device. Ofcourse, temperature sensors may be located at additional locations.

FIGS. 10A and 10B illustrates yet another preferred embodiment of thepresent invention, revealing two cross sectional drawings taken alongthe reference lines of A-A and B-B as labeled in FIG. 2. PSCC electrode170 extends from a catheter shaft 90, and PSCC electrode 170 comprises:a thermally conductive, electrically insulative, flexible shaft 173; aflexible inner conductive layer 171 (formed, for example, as a coatingand/or wrap around flexible shaft 173, or as illustrated in FIG. 10, ahelix); an outer PSCC substrate layer 172; a heat sink 175 thermallycoupled to flexible shaft 173; and a plurality of thermal sensors 174located within the thermally conductive, electrically insulative,flexible shaft 173 to measure temperatures at various locations therein.Electrically insulative flexible shaft 173 and flexible inner conductivelayer 171 may optionally include a portion of a sphere at theirrespective distal ends (as illustrated in FIG. 10A). Flexible innerconductive coil 171 is connected to an electrical conductor 114, whichmay be connected to an RF generator (e.g., RF current source 80). Inuse, this preferred embodiment is used to ablate tissue (not shown) towhich a reference electrode (not shown) has been attached. PSCCelectrode 170 ablates tissue by delivering ablation energy through theflexible inner conductive coil 171. Preferably, the reference electrodeis grounded to an electrical ground reference signal. As one of ordinaryskill can appreciate, temperature sensors 174 (such as thermistors,thermocouplers or other temperature sensors) can be used to monitoroperation temperature to help ensure effective and safe ablationtreatment. Heat sink 175 helps to prevent the electrode from overheatingthe electrode and the tissue.

Electrical conductor 114 may be implemented using a single conductivewire or multiple strands of wire. Preferably, the wires may be made offlexible conductive materials which allow the surface contacting area tobe bent and formed into various shapes to provide better contact to thetissue. Acceptable materials include, but are not limited to, stainlesssteel, nickel titanium (nitinol), tantalum, copper, platinum, iridium,gold, or silver, and combinations thereof. Preferably, the material usedto manufacture the conductive element is a bio-compatible electricallyconductive material, such as platinum, gold, silver, nickel titanium,and combinations thereof. Other electrically conductive materials coatedwith bio-compatible materials may also be employed, including forexample, gold-plated copper. Finally, it is also contemplated thatelectrically conductive polymers may also be used provided they arebio-compatible or coated with a bio-compatible material.

The present invention permits the construction of a flexible, pressuresensitive RF ablation electrode that can be used in a wide variety ofdifferent tissue environments, including for example, tissues havingvarying degrees of elasticity and contour.

The present invention permits the construction of a flexible electrodethat responds to pressure that is applied to the electrode, for example,pressure that may be applied to the electrode by the myocardium. Suchelectrodes may be used to respond to pressure that is applied directlyto the PSCC component (for example, when the PSCC component is locatedat the most distal portion of a catheter), or to pressure that isapplied indirectly to the PSCC (for example, when an electrode tip iddisposed between the PSCC component and the tissue). When used inconjunction with an electrode tip, it is desired that the electrode tipbe formed of a rigid, electrically conductive material. This will permitthe electrode tip to transfer pressure from the electrode tip to thePSCC component. Optionally, one or more additional pressure transferelements may be used, for example, between the electrode tip at a distalend and the PSCC component located at a more proximal end. In the casewhere a PSCC component is positioned within a catheter, the PSCCcomponent is preferably used to respond to pressure that is appliedaxially to catheter. Of course, the PSCC component could be oriented inorder to respond to pressure that is applied transversely to thecatheter.

While the preferred embodiments disclosed in the attached figuresdisclose an electrode that is generally cylindrical in shape, thepresent invention also contemplates that the electrode may be formedinto various shapes to better fit the contour of the target tissue. Inone embodiment, for example, the electrode can be made long enough tostrap around and form a noose around the pulmonary veins in epicardialapplications. Particularly, electrical conductor 114 that is coupled tothe RF energy source may be formed into a desired shape and then thePSCC layer will be formed over the conductive element in the preferredshape. For example, the electrode may be shaped like a spatula forcertain applications, including for example, minimally invasivesub-xyphoid epicardial applications, where the spatula shape will permiteasy placement and navigation in the pericardial sac. Because PSCC canbe made as a flexible material, it can be used for form electrodeshaving a great variety of shapes, including a spatula.

Alternatively, the electrically conductive element that is coupled tothe RF energy source (for example, 111, 121, 131, 141, 151, 161 and 171)may be formed using shape-memory retaining material, such as nitinol,which would permit the electrode to be fitted to specific presetgeometries, such as the ostium of a pulmonary vein, such that theelectrode is shaped to provide a desired contact pressure pattern on thetissue due to the deformation of the wire when pressed against thetissue.

Similarly, while the reference to insulative shaft (for example, 133,143, and 153) is generally used in connection with a generallycylindrical member, it is contemplated by the present invention that theinsulative shaft could be in a geometric shape other than a cylinder,including, for example, a noose, a spatula, or the shape of the ostiumof a pulmonary vein. For purposes of this application, the term“insulative shaft” is intended to encompass shapes in addition to acylindrical shaft.

Whenever it is desired that the conductive element that is coupled tothe RF energy source be formed in the shape of a helix, such as is thecase with elements 121, 131, 161 and 171, the coil may be chosen to beof a specific stiffness (i.e., having a characteristic spring constant)that would allow the coil to exert a desired amount of pressure on thePSCC when the electrode bends or deflects upon contact with the tissue.One of skill in the art would understand that the degree of desiredcontact pressure would depend in part upon the elastic property of thetissue being contacted with the electrode. For example, the atrial wallmay require less contact pressure than the ventricular wall. Thus,electrodes of varying stiffness can be designed for application indifferent tissues and different regions of the heart.

In some embodiments, for example, as depicted in FIGS. 5, 6 and 7, theconductive element may be mounted on an insulative shaft. The conductiveelement can be shaped in any number of ways, including for example, acoil, mesh, coating or wrap. The insulative shaft provides additionalmechanical support in applications that require greater amounts of axialforce and torque. The insulative shaft may be made of any electricallyinsulative material, including, for example, polyurethane. Preferably,the insulative shaft is made of a biocompatible, electrically insulativematerial.

Generally, flexibility is a very desirable characteristic in a catheter.Some applications, however, may require a less flexible and/or rigidcatheters. Thus, as an alternative to the flexible embodiments discussedabove, it is contemplated that the same structural design may be used toproduce a less flexible (or even rigid) ablation device. For example,the PSCC electrode may utilize a rigid core—instead of a flexible core.It may be solid conductive core of varying degrees of rigidity, or anon-conductive core coated with a conductive layer such that thecombination achieves a desired degree of rigidity. A PSCC substratelayer may then be applied to the core such that when the electrode ispressed against tissue, the PSCC becomes a conductor and electricallycouples the conductive core (or layer, as the case may be) to the tissuevia the PSCC. In this alternative embodiment, the PSCC may be coatedwith one or more outer electrically-conductive layers (which may berigid or flexible). In this further modification, the PSCC layer issandwiched between at least two conductive coatings, and thus underpressure, RF energy may be delivered to the tissue via the compressiblePSCC layer.

In other embodiments, for example, as depicted in FIGS. 8A and 9A, theconductive element is mounted on an electrically insulative butthermally conductive shaft. The thermally conductive shaft would improvethe cooling of the electrode and the electrode-tissue interfacetemperature during ablation by thermally conducting the heat from theinterface to the ambient flowing blood in endocardial applications. Inaddition, the thermally conductive shaft can be instrumented withthermal sensors (for example, as depicted in Exhibits 8 and 9) that canbe used for temperature controlled RF ablation. The thermally conductiveshaft may be made of any electrically insulative, thermally conductivematerial, including, for example, CoolPoly® thermally conductive,electrically insulative plastic. Preferably, the thermally conductiveshaft is made of a biocompatible, thermally conductive, electricallyinsulative material.

In yet another embodiment, for example, as depicted in FIG. 9, thecooling efficiency of the ablation electrode can be enhanced by mountinga heat sink 175 at the proximal end of the active electrode 170. Theheat sink comprises a material with high thermal conductivity. The useof a heat sink may be particularly useful for small electrodes typicallyaround 10 mm or less, or for sectioned electrodes that may give rise tohot spots. The heat sink may be made of any electrically insulative,thermally conductive material, including, for example, thermallyconductive polyurethane (e.g., polyurethane with thermally conductiveceramic powder embedded therein), diamond, aluminum nitride, boronnitride, silicone, thermal epoxy and thermally conductive, electricallyinsulative plastics. Preferably, the thermally conductive shaft is madeof a biocompatible, thermally conductive, electrically insulativematerial.

In yet another embodiment, the electrically insulative member maycontain one or more passageways for carrying cooling fluids (e.g.,saline solution) to the distal end of the electrode. Alternatively, oneor more of the passageways may be further defined by a cooling tube madeof the same material as, or a material different from, the insulativemember. If a cooling tube is used in addition to the passageway, theportion of the cooling tube that is located within the catheter shaft ispreferably thermally and electrically insulative, while the portion ofthe cooling tube that is located within the electrode is preferablythermally conductive. The thermally insulative tube inside the cathetershaft is to minimize the degree to which the cooling fluid is heated tobody temperature as the result of thermal conduction through thecatheter shaft wall as the fluid travels from the outside fluid sourcethrough the catheter shaft and to the electrode. The thermallyconductive tube inside the electrode, on the other hand, is intended tocool the electrode and the electrode-tissue interface during ablation bythermally conducting the heat from the interface to the flowing fluidinside the tube.

In yet another embodiment, the electrically insulative member maycontain one or more passageways for carrying cooling fluids to theactual electrode-tissue interface. The passageways include an inlet tothe electrode, and an outlet at the distal end of the electrode.Moreover, one or more thermal sensors may be placed in the passageway,for example, to measure the temperature of the coolant at the inlet andat the outlet. The temperature difference between the inlet and outletduring ablation could be used to monitor the efficacy of theelectrode-tissue interface cooling and also to performtemperature-controlled ablation. One or more of the passageways mayalternatively be further defined by a cooling tube, which is made bemade of the same material as, or a material different from, theinsulative member. If a cooling tube is used in addition to thepassageway, the portion of the cooling tube that is located within thecatheter shaft is preferably thermally insulative, while the portion ofthe cooling tube that is located within the electrode is preferablythermally and electrically conductive. The thermally insulative tubeinside the catheter shaft is to minimize the degree to which the coolingfluid is heated to body temperature as the result of thermal conductionthrough the catheter shaft wall as the fluid travels from the outsidefluid source through the catheter shaft and to the electrode. Thethermally conductive tube inside the electrode, on the other hand, isintended to cool the electrode and the electrode-tissue interface duringablation by thermally conducting the heat from the interface to theflowing fluid inside the tube.

FIG. 11 illustrates a specific preferred embodiment for the invention ofthe present application. PSCC electrode 180 extends from a cathetershaft 91 and is connected to an RF energy source (not shown). PSCCelectrode 210 further comprises coolant efflux hole 186 that permits thecoolant flowing through the core of the catheter from stagnating (andthus heating) inside the catheter. The efflux hole helps to ensure thata fresh supply of coolant is available to keep the working portion ofthe catheter cool. The use of efflux hole 186 could be utilized with anyof the preceding embodiments.

FIGS. 12A and 12B illustrate another preferred embodiment. Moreparticularly, FIGS. 12A and 12B illustrate the embodiment of FIG. 6, inwhich efflux hole 186 has been added. PSCC electrode 190 extends from acatheter shaft 91 and is connected to an RF energy source (e.g., RFcurrent source 80). PSCC electrode 190 comprises: flexible innerconductive coil 191 in the shape of a helix; an outer PSCC substratelayer 192; a thermally conductive, electrically insulative flexible tube193 located partially within the helix of the flexible inner conductivecoil 191; and a coolant efflux hole 196. Note that a thermallyinsulative tube 197 is used in at least a portion of the catheter shaft91 to help reduce the likelihood of cooling fluid 70 (e.g., salinesolution) being heated to body temperature. In this embodiment, notethat thermally conductive, electrically insulative flexible tube 193also forms the thermally conductive, electrically insulative, flexibleshaft which is present in other embodiments.

FIGS. 13A and 13B illustrate another preferred embodiment. Moreparticularly, FIGS. 13A and 13B represent a modified version of theembodiment of FIG. 12. PSCC electrode 200 extends from a catheter shaft91 and is connected to an RF energy source (e.g., RF current source 80).PSCC electrode 200 comprises: flexible inner conductive coil 201 in theshape of a helix; an outer PSCC substrate layer 202; a thermallyconductive, electrically insulative flexible tube 203 located partiallywithin the helix of the flexible inner conductive coil 201; a coolantefflux hole 206; and a plurality of thermal sensors 204 located withinthe thermally conductive, electrically insulative, flexible tube 203 tomeasure temperatures at various locations therein. Note that a thermallyinsulative tube 207 is used in at least a portion of the catheter shaft91 to help reduce the likelihood of cooling fluid 70 being heated tobody temperature. In this embodiment, note that thermally conductive,electrically insulative flexible tube 203 also forms the thermallyconductive, electrically insulative, flexible shaft which is present inother embodiments.

FIG. 14 illustrates yet another preferred embodiment for the inventionof the present application. More particularly, FIG. 14 is a modificationof the embodiment of FIG. 11. PSCC electrode 210 extends from a cathetershaft 91 and is connected to an RF energy source (not shown). PSCCelectrode 210 further comprises a heat sink 215 at the proximal end ofthe electrode and a coolant efflux hole 216 at the distal end of theelectrode.

FIGS. 15A and 15B illustrate yet another preferred embodiment. Moreparticularly, FIGS. 15A and 15B represent a modification of theembodiment of FIG. 12. PSCC electrode 220 extends from a catheter shaft91 and is connected to an RF energy source (e.g., RF current source 80).PSCC electrode 220 comprises: flexible inner conductive coil 221 in theshape of a helix; an outer PSCC substrate layer 222; a thermallyconductive, electrically insulative flexible tube 223 located partiallywithin the helix of the flexible inner conductive coil 221; a coolantefflux hole 226; and a heat sink 225 thermally coupled to flexible tube223. Note that a thermally insulative tube 227 is used in at least aportion of the catheter shaft 91 to help reduce the likelihood ofcooling fluid 70 being heated to body temperature. In this embodiment,note that thermally conductive, electrically insulative flexible tube223 also forms the thermally conductive, electrically insulative,flexible shaft which is present in other embodiments.

FIGS. 16A and 16B illustrate another preferred embodiment. Moreparticularly, FIGS. 16A and 16B a preferred embodiment, in which aclosed loop cooling system has been added. PSCC electrode 190 extendsfrom a catheter shaft 91 and is connected to an RF energy source (e.g.,RF current source 80). PSCC electrode 190 comprises: flexible innerconductive coil 191 in the shape of a helix; an outer PSCC substratelayer 192; a thermally conductive flexible shaft 198 located partiallywithin the helix of the flexible inner conductive coil 191; and closedloop cooling passageway 199 located within the flexible shaft 198. Notethat a thermally conductive, electrically insulative sleeve 194 mayoptionally be located between the flexible shaft 198 and innerconductive coil 191. It is contemplated that sleeve 194 may beeliminated, in which case the inner conductive coil 191 may be thermallycoupled directly to flexible shaft 198 and closed loop coolingpassageway 199. In this embodiment, thermally conductive flexible shaft198 and closed loop cooling passageway 199 form a closed loop coolingsystem in which a cooling fluid 70 (e.g., saline) may flow throughpassage way 199 to cool the distal tip of the catheter during ablation.

In an optional embodiment, any of the electrode designs above may becombined with a processor that monitors the RF current that is beingdelivered by the RF power source 80. In a preferred embodiment, acomputer processor (not shown) will monitor the maximum current beingdelivered and use this information to help control the ablation process.Because a PSCC's resistance drops monotonically as pressure increases,the amount of current being delivered can be used to assess a degree ofcontact between the contact surface 100 and tissue 12. Using thisinformation, the computer processor (not shown) may decrease or increasethe power level of the RF power source. By way of example only, thecomputer processor (not shown) may be used to limit the total amount ofRF energy that is delivered to a certain tissue area. Depending on thenature of the tissue, the power level may be increased to improve lesioncreation.

The PSCC used in the present invention may be chosen to be of a specificsensitivity. For example, highly sensitive PSCCs, which register a sharpchange in resistance with a finite amount of applied pressure, may bepreferred for soft contact applications such as the atrial wall. Lesssensitive PSCCs, which require more pressure to register the same amountof change in resistance, may be preferred for hard contact applicationssuch as ablation in ventricular walls.

The RF source to be used with the present invention is preferably withinthe radio frequency range of 200-800 kHz, and more preferably with 250kHz-550 kHz. The source is preferably capable of delivering up to 150Watts of electrical power.

The embodiments above may be manufactured in a variety of ways. One suchmethod involves forming an electrode assembly as follows. Anelectrically insulative shaft may be formed using known electricallyinsulative materials (which may be thermally conductive or thermallyinsulative). The shaft may be formed of flexible or rigid materials. Anelectrically conductive element for conducting RF energy may be formedon at least a portion of the electrically insulative shaft. Inaccordance with the teachings above, the conductive element may be madeto be flexible or rigid. A layer of PSCC may be formed over at least aportion of the conductive element, which PSCC material may be compressedunder pressure to become electrically coupled with the conductiveelement. In accordance with the teachings above, the electrode assemblymay be optionally coated with one or more conductive layers, which maybe either flexible or rigid depending on the application. Preferably,the optional layers are made of a biocompatible, electrically conductivematerial.

An alternative way to manufacture an electrode assembly of the presentinvention is as follows. An electrically conductive shaft may be formedusing known electrically insulative materials. The shaft may be formedof flexible or rigid materials. A layer of PSCC may be formed over atleast a portion of the conductive shaft, which PSCC material may becompressed under pressure to become electrically coupled with theconductive shaft. In accordance with the teachings above, the electrodeassembly may be optionally coated with one or more conductive layers,which may be either flexible or rigid depending on the application.Preferably, the optional layers are made of a biocompatible,electrically conductive material.

The electrode assemblies above may be formed a fluid lumen and an effluxhole to permit a cooling fluid to be delivered to the tissue duringablation. The assemblies may also be manufactured to include one or morethermal sensors using techniques that are applicable to other knowncatheter devices.

It is contemplated that each of the embodiments discussed above mayoptionally be used in connection with one or moreelectrically-conductive, outer coverings. Preferably, the outer coveringis electrically conductive, such as a flexible wire mesh, a conductivefabric, a conductive polymer layer (which can be porous or nonporous),or a metal coating. The outer covering may be used to not only increasethe mechanical integrity, but to enhance the PSCC device's ability toassess the tissue contact (for example, in the when measuring electricalcharacteristics using a reference electrode connected to the targettissue). In some cases, the outer covering may be made using abiocompatible material in order to help make the overall assemblybiocompatible. Preferably the outer covering is flexible, though certainapplications may prefer a medium to high degree of rigidity.

Other novel configurations using pressure sensitive conductive compositematerials are possible. FIGS. 17A-1C illustrate one such possibility.

A spring loaded, contact sensitive ablation assembly 300 is depicted inFIGS. 17A-17C. This device is especially useful for dry RF ablationtreatments. This embodiment includes: ablation electrode 310; PSCC pill320; shaft 330; flexible spring 340; conductive pin 350; and shaft 360.Ablation electrode 310 is preferably a 4-8 mm tip, blade or brush.Ablation electrode 310 and PSCC pill 320 may be inserted into shaft 330with the PSCC pill 320 preferably against the proximal end of electrode310 in the shaft 330. Shaft 330 may be covered with a heat shrink collar370, at or near a proximal end of shaft 330. A second heat shrink collar370 may be placed at the distal end of shaft 360. The heat shrinkcollars 370 may be used to help anchor the spring 340 for compressionsupport.

Conductive element 350 is preferably designed to deliver ablationenergy, such as RF energy to the ablation assembly 300. An external RFpower generator may, for example, be coupled to conductive pin 350 tomake the conductive pin a power source. Once the conductive pin 350(preferably made of copper) makes firm contact with the PSCC pill 320,RF power will flow through the PSCC pill 320 to electrode 310, andultimately be delivered to tissue. When there is no or only nominalpressure applied to electrode 310, the spring 340 will preventconductive pin 350 from contacting PSCC pill 320, and thus, no energywill be delivered to the tissue. As pressure increases, and sufficientpressure is applied to compress spring 340, conductive pin 350 will makecontact with PSCC pill 320, and as pressure continues to increase, PSCCwill be compressed with sufficient pressure between conductive pin 350and electrode 310, such that PSCC pill 320 will become conductive suchthat RF current will begin to flow. As PSCC pill 320 is compressedfurther, the impedance of PSCC pill 320 will continue to decrease, andthus, more RF current will pass. One can monitor the impedance and/orthe current being delivered and use this information to assess a degreeof contact between the electrode 310 and the tissue being treated. Forexample, as resistance decreases, which results in increases in current,the better contact is obtained. This embodiment also serves as a safetyfeature. Once you lift the spring-loaded assembly such that it is nolonger in compressed contact with a tissue surface, the RF power willautomatically shut off. As compression is decreased, the impedance ofPSCC pill 320 will increase which decrease the current flow and quicklyhalt the current flow entirely. Once pressure is decreased to the pointthat spring 340 no longer maintains compressed contact betweenconductive pin 350 and PSCC pin 320, the flow is precluded altogether bya gap in contact. This gap provides added assurances that RF current cannot be delivered in this uncompressed state. Moreover, the existence ofthe spring will help to reduce the possibility of arcing during ablationbecause it effectively breaks the conductive path for current flowingfrom the electrode to the tissue.

Acceptable materials for ablation electrode 310 include, but are notlimited to, stainless steel, nickel titanium (nitinol), tantalum,copper, platinum, iridium, gold, or silver, and combinations thereof.Preferably, the material used to manufacture ablation element 310 is abio-compatible electrically conductive material, such as platinum, gold,silver, nickel titanium, and combinations thereof.

In a variation of this embodiment, one can compress the spring bypressing down on a knob from the proximal end of the device. Much likehow the knob on a retractable pen extends the ball point into a writingposition, the knob on this variation will place the conductive pin inconductive contact with the PSCC pill. Preferably, the knob will forcethe conductive pin to compress down along with the spring and will makefirm contact with the PSCC pill, such that the PSCC pill is conductive.More preferably, the amount of RF current may be controlled by theamount of pressure being applied to the knob at the proximal end of thedevice.

One of ordinary skill will appreciate that while the PSCC materials maybe designed to respond to a variety of stresses, the principles andembodiments herein may be adapted to respond to specific stress forces,for example, axial forces, orthogonal forces, twisting, compressing,stretching, etc., without deviating from the scope of the presentinvention. Furthermore, one of ordinary skill will appreciate that byusing springs having different spring constants, additional flexibilitycan be designed into a spring-loaded PSCC ablation device.

Although multiple embodiments of this invention have been describedabove with a certain degree of particularity, those skilled in the artcould make numerous alterations to the disclosed embodiments withoutdeparting from the spirit or scope of this invention. All directionalreferences (e.g., upper, lower, upward, downward, left, right, leftward,rightward, top, bottom, above, below, vertical, horizontal, clockwise,and counterclockwise) are only used for identification purposes to aidthe reader's understanding of the present invention, and do not createlimitations, particularly as to the position, orientation, or use of theinvention. Joinder references (e.g., attached, coupled, connected, andthe like) are to be construed broadly and may include intermediatemembers between a connection of elements and relative movement betweenelements. As such, joinder references do not necessarily infer that twoelements are directly connected and in fixed relation to each other. Itis intended that all matter contained in the above description or shownin the accompanying drawings shall be interpreted as illustrative onlyand not limiting. Changes in detail or structure may be made withoutdeparting from the spirit of the invention as defined in the appendedclaims.

1. An electrode assembly comprising: a conductive pin for conductingablation energy; an ablation electrode at a distal end of the electrodeassembly; and a pressure sensitive conductive composite element disposedbetween the conductive pin and the ablation electrode; said pressuresensitive conductive composite element being positioned such that whenit is compressed between the conductive pin and the ablation electrode,the pressure sensitive conductive composite element conducts ablationenergy from the conductive pin to the ablation electrode.
 2. Theelectrode assembly of claim 1 further comprising: a first shaft in whichthe ablation electrode is disposed at a distal end; a second shaft inwhich the conductive pin is disposed; and a spring that permits thefirst and second shafts to be compressed toward each other.
 3. Theelectrode assembly of claim 2 further comprising: a collar on each ofthe first and second shafts such that the spring may be anchored betweenthe two collars during compression.
 4. The electrode assembly of claim 2wherein the pressure sensitive conductive composite element comprises aquantum tunneling composite material.
 5. A catheter assembly forconducting ablative energy, said assembly comprising: a catheter bodyhaving an ablation electrode; and a pressure sensitive conductivecomposite member; a conductive pin for conducting ablation energy; and aspring that is capable of being in at least a first state and a secondstate, said first state being one in which the spring electricallydecouples the electrode from at least one of the conductive pin and thepressure sensitive conductive composite member; and said spring beingcompressible into a second state wherein pressure is applied to thepressure sensitive conductive composite member to place it in aconductive state, thereby transferring ablation energy from theconductive pin to the ablation electrode.
 6. The catheter assembly ofclaim 5, wherein the ablation electrode is located on a distal end ofthe catheter assembly, and wherein the pressure sensitive conductivemember is disposed in physical contact with the electrode along thelongitudinal axis of the electrode assembly.
 7. The catheter assembly ofclaim 5, further comprising at least one pressure transfer memberdisposed between the pressure sensitive conductive composite member andthe ablation electrode, such that pressure applied to the ablationelectrode is transferred through the at least one pressure transfermember to the pressure sensitive conductive composite member.
 8. Thecatheter assembly of claim 5 further comprising: a collar on each of thefirst and second shafts such that the spring may be anchored between thetwo collars during compression.
 9. A method of treating tissue, themethod comprising: providing an electrode assembly having: a conductiveelement for conducting RF energy; an ablation electrode at a distal endof the electrode assembly; and a pressure sensitive conductive compositemember disposed between the conductive element and the ablationelectrode; positioning the electrode assembly in contact with a tissueto be treated; exerting sufficient force upon the tissue through theelectrode assembly such that the pressure sensitive conductive compositemember becomes conductive and permits the delivery of RF energy to thetissue.
 10. The method of claim 9, wherein at least two of theconductive element, the ablation electrode and the pressure sensitiveconductive composite element are electrically decoupled, the methodfurther comprising: moving at least one of the conductive element, theablation electrode and the pressure sensitive conductive compositeelement to electrically couple the conductive pin, the pressuresensitive conductive composite element and the ablation electrode, suchthat ablation energy may be delivered from the conductive pin to theablation electrode via the pressure sensitive conductive compositeelement.
 11. The method of claim 9, further comprising: measuring theresistance along a path of pressure sensitive conductive compositemember; generating a signal that is indicative of the measuredresistance having dropped below a set threshold, thereby indicating adesired level of contact between the pressure sensitive conductivecomposite material and the tissue.
 12. The method of claim 9, furthercomprising: using a generator to deliver RF energy to the conductiveelement, said generator having a switch to control delivery of RFenergy; measuring the resistance along a path of pressure sensitiveconductive composite member; generating a signal that is indicative ofthe measured resistance having dropped below a set threshold; waiting apredetermined period of time; and controlling the switch of thegenerator to turn off the RF energy.
 13. The method of claim 9, furthercomprising: using a generator to deliver RF energy to the conductiveelement, said generator having a switch to control delivery of RFenergy; monitoring at least one of the generator and the catheter todetermine when delivery of RF energy to the tissue has commenced andgenerating a signal to indicate that delivery of RF energy hascommenced; waiting a predetermined period of time; and controlling theswitch of the generator to turn off the RF energy.
 14. The method ofclaim 9, wherein the electrode assembly is being using to ablate tissuewithout any external fluid being added, and wherein at least two of theconductive element, the ablation electrode and the pressure sensitiveconductive composite element are electrically decoupled, the methodfurther comprising: moving at least one of the conductive element, theablation electrode and the pressure sensitive conductive compositeelement to electrically couple the conductive pin, the pressuresensitive conductive composite element and the ablation electrode, suchthat ablation energy may be delivered slowly via the pressure sensitiveconductive composite element so as to mitigate the effects of arcing.15. An electrode assembly comprising: a conductive pin for conductingablation energy; an ablation electrode at a distal end of the electrodeassembly; a pressure sensitive conductive composite element disposedbetween the conductive pin and the ablation electrode; and an engagementassembly that moves at least one of the conductive pin, the pressuresensitive conductive composite element and the ablation electrode tocreate an engagement position and a non-engagement position, wherein theengagement position electrically couples the conductive pin, thepressure sensitive conductive composite element and the ablationelectrode, such that ablation energy may be delivered from theconductive pin to the ablation electrode via the pressure sensitiveconductive composite element; and wherein the non-engagement positionelectrically decouples at least two of the conductive pin, the pressuresensitive conductive composite element, and the ablation electrode, suchthat ablation energy is not delivered to the ablation electrode.
 16. Theelectrode assembly of claim 15 wherein the engagement assemblycomprises: a first shaft in which the ablation electrode is disposed ata distal end; a second shaft in which the conductive pin is disposed;and a spring that permits the first and second shafts to be compressedtoward each other.
 17. The electrode assembly of claim 16 furthercomprising: an anchor on each of the first and second shafts such thatthe spring is secured between the two anchors during compression. 18.The electrode assembly of claim 16 wherein the pressure sensitiveconductive composite element comprises a quantum tunneling compositematerial.